Gemini generateContent (base tier)

Google's native generateContent wire on the base tier. Send POST /v1/gemini with the required field contents and pay quoted per request from $0.020 over x402 or MPP (there is no free tier). It returns a JSON object with candidates, usageMetadata and modelVersion.

Send Gemini's own request shape (contents, systemInstruction, generationConfig, function declarations) and get Gemini's own response shape (candidates, usageMetadata) back. Point a Google GenAI SDK at this gateway and pay per request with USDC, no account. Also answers the Google-shaped path /v1beta/models/<model>:generateContent.

Category: LLM gateway · Tags: llm gemini google generatecontent chat

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Parameters

Example request

curl -i -X POST https://agent402.tools/v1/gemini \
  -H "Content-Type: application/json" \
  -d '{"contents":[{"role":"user","parts":[{"text":"Summarize x402 in one sentence."}]}],"generationConfig":{"maxOutputTokens":256}}'

Without payment this returns HTTP 402 Payment Required with the exact price for v1-chat-gemini; any x402 v2 or MPP client pays it and retries.

Example response

{
  "candidates": [
    {
      "content": {
        "role": "model",
        "parts": [
          {
            "text": "x402 is an HTTP-native way for agents to pay per request with USDC."
          }
        ]
      },
      "finishReason": "STOP",
      "index": 0
    }
  ],
  "usageMetadata": {
    "promptTokenCount": 14,
    "candidatesTokenCount": 18,
    "totalTokenCount": 32
  },
  "modelVersion": "google/gemini-3.5-flash-lite"
}

From an MCP client

catalog.call {
  "slug": "v1-chat-gemini",
  "params": {
    "contents": [
      {
        "role": "user",
        "parts": [
          {
            "text": "Summarize x402 in one sentence."
          }
        ]
      }
    ],
    "generationConfig": {
      "maxOutputTokens": 256
    }
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for v1-chat-gemini; the stdio package pays it from a wallet or from AGENT402_CREDITS_KEY. Local install: npx -y agent402-mcp.

Errors and behavior

• contents is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Wallet-only: this tool runs a model, so it has no proof-of-work tier. A prepaid card-credits key issued earlier (Authorization: Bearer a402_...) also pays it.
• Model-backed: the answer is generated by a model, so the same input can produce different wording.
• Priced per request: the 402 quotes this body, between $0.020 and $0.5.
• Flat per call for the models this tier serves. A body naming another flat tier's model (nano, base, pro, premium) is quoted at that tier's price in the 402 and served under that tier; model "auto" is quoted and served as the auto tier. The answer names the tier in agent402_tier. The live 402 is always the price.
• A GET or HEAD to /v1/gemini returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB and a streamed response are not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/v1/gemini", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "contents": [
      {
        "role": "user",
        "parts": [
          {
            "text": "Summarize x402 in one sentence."
          }
        ]
      }
    ],
    "generationConfig": {
      "maxOutputTokens": 256
    }
  }),
});

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